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Full text of "Circuits"

Dish-O-Tron 6000 



Make] Projects 



Dish-O-Tron 6000 



Written By: Quinn Dunki 



PARTS: 

Resistor (4) 

Resistor (2) 

Resistor (1) 

Trim Pot (1) 

Trim Pot (1) 

Thermistor (1) 

Capacitor (2) 

Capacitor (1) 

Capacitor (1) 

Transistor (2) 

Switch (2) 

Switch (1) 

Switch (1) 

LED (2) 

555 Timer IC (2) 

9 Volt alkaline battery (1) 

Header (1) 

Too much free time (1) 



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Dish-O-Tron 6000 



SUMMARY 

I'm absent minded in general, but especially when it comes to the dishwasher. I can never 
remember whether the dishes are clean, whether the machine needs to be run, or emptied, 
or whatever. I needed a solution to this problem. My first thought was to hang a flippable 
sign on the door that said "clean" on one side, and "dirty" on the other. Simple, logical, 
functional. My second thought was, "What?!? That's dangerously under-engineered. I can 
make something much more ridiculous than that". 

This contraption is the result. 



Step 1 — Dish-O-Tron 6000 




• The challenge here is to automatically detect when the machine is running (so we know 
when dishes have been cleaned), and to automatically detect when the machine has been 
unloaded (so we know when the dishes inside are dirty once again). 

• For more detail and better pictures, see: BlondiHacks - Dish-O-Tron 6000 



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Dish-O-Tron 6000 



Step 2 




• Here's a video showing the Dish-O-Tron 6000 in action! YouTube link 

• As you can see, all you do is slap it on the door, and turn it on. Then use your dishwasher 
as you normally would! It's brilliant!* 

• *Product may not actually be brilliant. Void where prohibited. 



Step 3 




• To determine when the dishes are 
clean, we need to know when the 
machine runs. This is done by 
detecting the temperature of the 
door panel. When the machine 
runs, it gets quite warm. 

• In this photo you can see the small 
blue thermistor sticking out the 
back, which contacts the 
dishwasher's front panel. 

• You can also see the magnets that 
hold the Dish-O-Tron securely to 
the front of the machine. 



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Dish-O-Tron 6000 



Step 4 




• Next we need to know when the 
machine has been unloaded (which 
means the contents are dirty once 
again). 

• This is a bit tricky, because we 
need to distinguish between 
grabbing a quick dish or two (thus 
leaving the machine full but still 
clean), versus unloading the 
machine completely. This is done 
by detecting when the door is fully 
open (using a rolling-ball tilt 
switch), then waiting a full minute. 
If the door is open that long, it's 
because I'm unloading it. If the 
door only opens part way, or only 
opens briefly, I'm probably just 
grabbing a clean bowl for my 
cereal, but don't feel like unloading 
the machine right now. 



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Dish-O-Tron 6000 



Step 5 




• So, here's the schematic! 

• The upper 555 is configured 
bistable, and tracks the state of the 
dishes (Clean or Dirty). The initial 
state is Dirty. The 3103 thermistor 
forms a voltage divider that pulls 
pin 2 low enough to flip the state 
when the machine gets warm. The 
lower 555 is configured astable. It 
starts timing when the tilt-switch is 
closed, and if a minute passes 
without the tilt-switch opening 
again, the upper 555's state is 
reset again. Simple! 



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Dish-O-Tron 6000 



Step 6 




fDish-o-Tron 6000 
'SOU OuinnDunk, 
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• Here's the schematic with the 
functional units marked. 

• You can see there are also manual 
controls for setting the state, since 
there are bound to be cases where 
the device gets out of sync with the 
real world. Also note that the Dirty 
state is just the inverse of the 
Clean state. The device really only 
tracks whether the dishes are 
Clean. The lower 555 is only 
enabled when the upper 555 is in 
the Clean state. If the dishes are 
dirty, I don't care what the door is 
doing. The unloading timer's RC 
circuit has a trim pot in it, so I can 
tune it if I find that I unload the 
machine quicker or slower than 
expected. 



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Dish-O-Tron 6000 



Step 7 




• With the basic design settled, the 
next step was to figure out the 
voltage divider for the thermistor. 
For that, I needed to know how 
warm my dishwasher gets. I ran a 
full cycle with a 31 03 taped to the 
door, and kept an eye on the 
resistance. 



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Dish-O-Tron 6000 



Step 8 









31Q3P K »fil.ForO»DM»«.l H rc y el. 




















— ; o ^-- 



• Using that setup, I graphed the 
results to determine a good trigger 
point. The trick is that it still has to 
work when the ambient 
temperature is high (such as in 
August, since I have no A/C). That 
means trying to choose the hottest 
point in the cycle, with a bit of 
margin for error. 

• I believe that graphing the 
temperature profile of my 
dishwasher may in fact be the 
dorkiest thing I have ever done. 

• I decided to set the cut-off at 7.5k. 
That's close to as hot as the 
machine gets, and it represents 
about 33 °C, which is hotter than 
my kitchen ever gets. Just in case 
though, the voltage divider has a 
trim pot in it that provides lots of 
room to play with this. 



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Dish-O-Tron 6000 



Step 9 




• The next step was to breadboard it 
and test it in real-world conditions. 
I had bench-tested it prior to this, 
using a 10k pot to simulate the 
thermistor, and a toggle to simulate 
the tilt-switch. 



Step 10 




• Once it was working on the breadboard, I soldered it up, and tested the real circuit. The 
little metal can is the rolling-ball tilt switch, mounted outboard on some stiff wire so that the 
angle can be adjusted as needed. 

• That is some ghetto soldering right there, kids. Do try this at home, but as you can see, I 
am not a trained professional. Well, I am a trained professional smartass*, just not a 
trained professional solderererererer. 

• * "Trained Professional Smartass" is not a thing you can be. Void where prohibited. 



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Dish-O-Tron 6000 



Step 11 




• Once the PCB was done, I bench- 
tested it by sticking LEDs in the 
header connection, and again 
simulating the thermistor with a 10k 
pot. This time I'm using the real tilt 
switch, hence the hilarious angle I 
needed to get the helping-hands up 
to. Well, I thought it was hilarious. 
Unconventional angles are funny. 
Shut up. No, YOU shut up. 



Step 12 




• For the casing, I decided to gut a 
broken old Palm Pilot that a friend 
gave me. It's about the right form 
factor, and it has nice holes 
already well-placed for the I/O 
elements. I mounted magnets to 
stick it to the dishwasher, and the 
thermistor sticks through a crack in 
the original battery hatch such that 
it contacts the door panel. 



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Dish-O-Tron 6000 



Step 13 




• I built a chassis harness with all 
the I/O elements, and routed it to a 
header on the PCB. This way the 
PCB is removable, in case I ever 
want to futz with it some more. 



Step 14 




» Next I test-fit everything, and did a 
full chassis shakedown. Holding a 
soldering iron near the thermistor 
(no touchy!!) did a nice job of 
simulating a dishwasher cycle. 



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Dish-O-Tron 6000 



Step 15 




• I modified the shell a bit to suit my 
needs, then gave it a nice coat of 
white to match the dishwasher. An 
old wire hanger makes a nice 
painting jig. 



Step 16 




• There you have it! The Dish-O-Tron 
6000. It was fun to build, and might 
be the most ludicrously over- 
engineered way to solve this 
simple problem. That's why I love 



it. 



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Dish-O-Tron 6000 



Step 17 




• In closing, I'd like to mention that 
the development of this wasn't 
nearly the smooth path that it might 
appear to have been from reading 
this. In fact, I went through a bunch 
of designs before settling on this 
one. Simplicity can be a difficult 
goal to reach. At its worst, the 
design had four(!) 555 ICs, 
managing six(!) states. I swear it 
made sense at the time. Talk about 
over-designed. Here it is on the 
breadboard, where it stayed, 
because I never actually got this 
version to work. 

• In addition to being over-designed, 
this approach had fundamental 
issues that would have kept it from 
ever working. It was like the 
mechanical difference engine of 
dishwasher state detectors. 

• So why am I including this 
information? Hey, any excuse for 
breadboard prOn. Aww, yeah. 

• If you made it this far, thanks for 
reading! 

• You should also check out One 
Girl, One Laptop Productions . Help 
me pay for more hacks! 



This project assumes some basic knowledge of electronics, but nothing super fancy. You could 

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Dish-O-Tron 6000 

easily build it without knowing how it works. 

This document was last generated on 2012-11-02 11:38:35 PM. 



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